mmc: of_mmc_spi: Add IRQF_ONESHOT to interrupt flags

If no primary handler is specified for threaded_irq then a
default one is assigned which always returns IRQ_WAKE_THREAD.
This handler requires the IRQF_ONESHOT, because the source of
interrupt is not disabled

Signed-off-by: Saurabh Sengar <saurabh.truth@gmail.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>